AIN SHAMS UNIVERSITY
FACULTY OF ENGINEERING
International Credit Hour Programs (iCHEP)
Senior 1 Level, Communication Systems Eng. Program
Fall, 2021/2022
Course Code: ECE__354 / ECE 354
Time allowed: 2 Hrs.
Digital Communications
The Exam Consists of Four Questions in Two Pages.
Maximum Marks: 40 Marks
Important Rules:
• Having a )mobile -Smart Watch- earphones) inside the examination
hall is forbidden and is considered as a cheating behavior.
• It is forbidden to have any references, notes, books, or any other
materials even if it is not related to the exam content with you in the
examination hall.
Question 1.
1/2
‫تعليمات هامة‬
‫ل‬
‫ سماعة األذن) داخل‬- ‫ الساعات الذكية‬- ‫• حيازة (املحمو‬
. ‫لجنة المتحان يعتبر حالة غش تستوجب العقاب‬
‫• ليسمح بدخول أي كتب أو مالزم أو أوراق داخل اللجنة‬
.‫واملخالفة تعتبر حالة غش‬
(10 Marks)
a) A speech signal has a total duration of 10 s and bandwidth of 4 KHz, is to be transmitted via PCM
system. It is sampled at the Nyquist rate and then encoded. The signal-to-quantization noise ratio is
required to be 40 dB. Calculate the minimum storage capacity needed to accommodate this digitized
speech signal.
[3 Marks]
b) Repeat part (a) for a video signal of 5 MHz bandwidth.
[3 Marks]
c) Comment on the results of parts (a) and (b)
[1 Marks]
d) Sketch the PCM transmitter and receiver block diagrams.
[3 Marks]
Question 2.
(8 Marks)
An 4-Ary PAM wave is to be transmitted over a baseband channel with an absolute maximum bandwidth
of 800 kHz. The bit duration is 0.5 µs. Find a maximum and minimum values of the raised-cosine filter
rolloff factor that can be used. In both cases, sketch the raised-cosine spectrum.
Question 3.
(10 Marks)
It is required to select two orthonormal functions, over a period T, from the following three functions.
Examine these functions to determine which pair of them can be used,
 1
 T

a) x1 (t ) = 
0


 1
 T

 1
b) x 2 (t ) = −
 T
0


 2
 2 
sin 
t

 T 
 T

c) x3 (t ) = 
0


0t T
elsewhere
0t
T
2
T
t T
2
elsewhere
0t T
elsewhere
AIN SHAMS UNIVERSITY, FACULTY OF ENGINEERING
International Credit Hour Programs (iCHEP), Senior 1 Level, Communication Systems Eng. Program
Fall, 2021/2022
Course Code: ECE__354 / ECE 354
Time Allowed: 2 Hrs.
Digital Communications
The Exam Consists of Four Questions in Two Pages.
Question 4.
2/2
(12 Marks)
The input binary sequence 1100100010 is passed through a QPSK transmitter described by the below
equation, where T is the symbol period and i=1, 2, 3, and 4. Draw the signal space diagram of this system
and sketch the following waveforms
 2E


cos  c t + (2i − 1) 

4

 T

si (t ) = 
0


a) In-phase and quadrature baseband signals.
b) In-phase and quadrature modulated signals.
c) The QPSK signal.
0t T
elsewhere
[4 Marks]
[4 Marks]
[4 Marks]
END of Exam, Good Luck
Examination Committee
Prof. Hussein Abd El Atty Elsayed
Exam. Date : 30th of Jan,2022
AIN SHAMS UNIVERSITY, FACULTY OF ENGINEERING
International Credit Hour Programs (ICHEP), COMMUNICATION SYSTEMS ENGINEERING PROGRAM
Fall 2019
Course Code: ECE 354 / COMM 483
Time Allowed:3 Hrs.
Digital Communication Systems
The Exam Consists of Five Questions in Eight Pages.
Question 1.
2/8
(8 Marks)
a) Sketch both of the PCM transmitter and receiver block diagrams.
[2 Marks]
b) A binary PCM system, that uses polar NRZ signal, operates just above the error threshold with an
average probability of error equal to 10-6. Suppose that the pulse width is doubled, find the new
value of the average probability of error.
[2 Marks]
c) Explain what happens in the probability of error if the probability of one is increased while the
receiver threshold is in the middle.
[2 Marks]
d) If the probability of error of part (c) is returned to the original value by changing the pulse width,
find the required pulse width.
[2 Marks]
AIN SHAMS UNIVERSITY, FACULTY OF ENGINEERING
International Credit Hour Programs (ICHEP), COMMUNICATION SYSTEMS ENGINEERING PROGRAM
Fall 2019
Course Code: ECE 354 / COMM 483
Time Allowed:3 Hrs.
Digital Communication Systems
The Exam Consists of Five Questions in Eight Pages.
Question 3.
5/8
(6 Marks)
It is required to select two orthonormal functions, over a period T, from the following three functions.
Examine these functions to determine which pair of them can be used,
 1
 T

x1 (t )  
0


 2
 2 
sin 
t

T
 T 


x3(t )  
0


0t T
elsewhere
0t T
elsewhere
 1
 T

 1
x 2 (t )  
 T
0


0t 
T
2
T
t T
2
elsewhere
AIN SHAMS UNIVERSITY, FACULTY OF ENGINEERING
i-CREDIT HOURS ENGINEERING PROGRAMS, Communication Engineering Program
Course Code: CSE367
Digital Image Processing
Fall Semester 2019
Time Allowed: 3 Hrs.
The Exam Consists of Four Questions in Three Pages.
2/3
4) Calculate the entropy and the bpp (bits per pixel) of the image after Huffman Coding.
(b) What is the practical advantage of using the dictionary techniques compared to the Huffman
coding? [2 marks]
(c) A sequence is encoded using the LZW algorithm and the initial dictionary shown in the
following table: [4 marks]
Index
1
2
3
4
5
6
Entry
a
b
h
i
s
t
The output of the LZW encoder is the following sequence:
6
3
4
5
2
3
1
6
2
9 11 16 12 14
4 20 10
8 23 13
Decode that sequence.
Question (3): [8 marks]
(a) You are required to design a detector for curved objects whose boundaries in the
image can be expressed with the equation 𝑦 = 𝑎𝑥 2 + 𝑏𝑥 + 𝑐. You are considering
using the Hough transform algorithm to solve the problem.
1) What is the dimensionality of the Hough space?
2) What is the shape of the object in the Hough space corresponding to a point in the
image space?
3) In the special case where the parameter 𝑎 is known to be 0, the object in Hough
space corresponding to a point in the image space reduces to which shape.
4) In the special case where the value of the parameter 𝑐 is known to be 𝑐0 , the object
in Hough space corresponding to a point in the image space reduces to which
shape.
AIN SHAMS UNIVERSITY, FACULTY OF ENGINEERING
International Credit Hour Programs (ICHEP), COMMUNICATION SYSTEMS ENGINEERING PROGRAM
Fall 2019
Course Code: ECE 354 / COMM 483
Time Allowed:3 Hrs.
Digital Communication Systems
The Exam Consists of Five Questions in Eight Pages.
Question 5.
7/8
(8 Marks)
The input binary sequence 1100100010 is passed through a QPSK transmitter described by the below
equation, where T is the symbol period and i=0, 1, 2, and 3, which equals the numeric value of the
corresponding bits; then,
 2E


cos  c t  2i  1 

T
4



si (t )  
0


a)
b)
c)
d)
Note:

0t T
elsewhere
Draw the signal space diagram of this system
Sketch the in-phase and quadrature baseband signals
Sketch the in-phase and quadrature modulated signals
Sketch the QPSK signal
Indicate the appropriate values of the signal level and time in all waveforms.
[2 Marks]
[2 Marks]
[2 Marks]
[2 Marks]
‫جامعة عين شمس‬
‫كليـة الهندسة‬
‫برامج الساعات المعتمدة‬
Faculty of Engineering
Credit Hours Engineering Programs
COMM 483: Digital Communication Systems
Final Exam: Summer 2015
Dr. Hussein Abd El Atty Elsayed
Communication Systems Eng. Prog
Examination’s duration: 3 hr
Page 1/2
The exam consists of 5 questions in 2 pages.
Question 1.
(8 Marks)
The input of a PCM transmitter is m(t)=4sin(2000t) and the sampling rate is 5000 samples/sec
(the first sample starts at t=0). The relationship of the quantizer output, y(t), and input, x(t), is as
follows,
y(t)=n-1/2
n-1<x(t)≤n,
Where n is the level number, and n takes values –3,-2,-1,0,1,2,3,4. The encoder table is as
shown below,
Level
3.5
2.5
1.5
.5
-.5
-1.5
-2.5
-3.5
Code
000
001
010
011
100
101
110
111
a) Draw the PCM transmitter block diagram.
b) Draw the quantizer transfer function.
c) Sketch the waveform after each block of the PCM transmitter (draw the signals
underneath each other for only one cycle of the input signal)
d) Write down the bit stream of the PCM output (for only one cycle of the input signal).
e) Find the signal-to-noise ratio at the quantizer output.
Question 2.
(8 Marks)
a) An 4-Ary PAM wave is to be transmitted over a baseband channel with an absolute
maximum bandwidth of 800 kHz. The bit duration is 0.5 µs. Find a maximum and minimum
values of the raised-cosine filter rolloff factor that can be used. In both cases, sketch the
raised-cosine spectrum.
b) Consider a sine wave of frequency fm and amplitude Am, which is applied to a delta
modulator of step size ∆. Show that slope-overload distortion will occur if Am > ∆/(2πfmTs),
where Ts is the sampling period. What is the maximum power that may be transmitted
without slope-overload distortion?
Final Exam: Summer 2015
Question 3.
COMM 483: Digital Comm. Systems
(8 Marks)
Determine the matched filter of the signal s(t)=t
maximum value of the output signal.
Question 4.
Page 2/2
0<t<1 ms and zero otherwise. Then find the
(8 Marks)
a) Show whether or not x1 and x2 are orthonormal functions, over a period 1 msec, where
x1(t )  cos2000t  and x2 (t )  cos2500t  in 0  t  1 m sec with period T. Are they
basic orthonormal functions? Why?
b) Sketch the constellation diagram, transmitter, and receiver of the binary FSK systems
Question 5.
(8 Marks)
The input binary sequence 1100100010 is passed through a QPSK transmitter described by the
below equation, where T is the symbol period and i=1, 2, 3, and 4. Draw the signal space
diagram of this system and sketch the following waveforms
 2E


cos  c t  2i  1 

4

 T

si (t )  
0


0t T
elsewhere
a) In-phase and quadrature baseband signals.
b) In-phase and quadrature modulated signals.
c) The QPSK signal.
With Success